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Let's Talk Tunnel Rams (Yes again)

Zack

Member
Hey guys as most of you know i have been having some rich/tuning issues lately on my (Tunnel Ram) engine. Carbs are both stock Edelbrock 600's with mechanical secondaries. My question is one that Ted addressed in another thread to some degree.

1. If i disable the front carb, will that improve my running rich issue?

2. What will be any negative effects disabling one carb will have on the engine and performance?

3. Should i stick with both carbs operational and just keep trying to hit the right tuning combo?

4. Would disconnecting the secondaries help?
 
Zack: Are you currently running a progressive linkage? Both Dad and I have dual quads with 500 edelbrocks and are running edelbrocks progressive linkage. His is a mild 350 and I have a mild 302. Both are adjusted so the front carb only opens under heavy throttle. Most of the time the back carb does all the work. I've put several thousand miles on mine in the last couple years and besides the bent needle issue, it runs pretty well considering its waaaay over carb'd!
 
Hey Ben. I am running a direct linkage from Enderle. Both carbs working together as one. It just washed out (fouled) my plugs and i don't want to do that again. However, i did adjust the floats since then but it is still running too rich in my opinion. When the exhaust fumes are so strong it burns my eyes it is time to adjust something, LOL.

4003-2.jpg
 
I would seriously consider running a progressive linkage... they are about $50 from Summit and you can easily adjust when the front carb kicks in.

I don't have a great pic of my setup--here is the best I could find:
DSC00248-1.jpg
 
Call Edelbrock tech line Monday morning. Its free. Tell the tech line everything, don't fudge or exaggerate. Tell them all the particulars about your engine. If you don't know, call your engine builder. That's what the tech line is there for.
 
Yes I would wait till you get the regulator and set the fuel pressure down to 5 psi. Then if you still are too rich call Edelbrock. I run 2 Edel on the blower motor with straight linkage and no problems. I bought both carbs new and followed Edel build specs for a blower motor. I sure hated tearing apart 2 brand new carbs and replacing all kinds of stuff inside, but it worked out fine. For what it is worth I run 6 psi on my set up.
 
Zack, you're asking a lot of the same questions you were asking in the other thread.

What you're missing in the equation is that you need to provide some answers to some of the questions others have asked you.

Hey guys as most of you know i have been having some rich/tuning issues lately on my (Tunnel Ram) engine. Carbs are both stock Edelbrock 600's with mechanical secondaries. My question is one that Ted addressed in another thread to some degree.
Those were 500 CFM carbs in the other thread. Are they now, in fact, 600 CFM models?

You need to understand two facts. 1. That intake was not designed to be used on a street-driver. 2. You have far too much carburetor for what you're trying to do. You cannot escape those facts. All you can do is try to make things work as well as possible.

Step Number 1 - Quit trying to second-guess things.
Step Number 2 - Start testing things, so you will have hard data to work with, instead of guesses, ideas and generalities.

1. If i disable the front carb, will that improve my running rich issue?

Answer? Who knows? Have you checked fuel pressure, to verify it is set at 6 psi or lower? Because that is quite likely the root of all your problems. But there is no way to know that for sure, because nobody knows where it is currently set.

So how can you change something, when you have absolutely no idea that is the cause of the problem?

2. What will be any negative effects disabling one carb will have on the engine and performance?

Losing fuel balance to various cylinders. The common plenum on your intake choice will cover up some of the problem, but not all of it. You hide a lot of it by running on the rear carb alone, rather than the front carb alone, but balance will be affected.

If you feel disabling the front carb is the fix for your combination, you be absolutely sure you lock the throttle blades in the closed position. Otherwise, you're going experience over-heating, running lean and have all the fixings for a run-away motor.

3. Should i stick with both carbs operational and just keep trying to hit the right tuning combo?

You can tune what you have, so it will work reasonably well. Would you walk into a restaurant and order two steak dinners, when you have intentions of eating only one?

4. Would disconnecting the secondaries help?

The mechanical secondaries on an Edelbrock carb shouldn't be confused with the mechanical secondary Holley carbs, which also use a secondary crutch, errr, accelerator pump. The secondary side of an Edelbrock carb is not going to flow any air/fuel until the weighted, secondary air valve opens.

Here are some specific questions for you -

1. Have you verified your fuel pressure setting? If not, why in the Dickens are you trying to sort what your problem might be? The problem might be (and likely is) excessive fuel pressure.

2. You said the engine builder ran this engine on a dyno or a test stand and that it ran fine. Did you have eyes and ears on this test session, or are you taking the engine builder's word at face-value?

3. You said the engine builder ran the engine with his intake. What intake was that? And what carburetor/s did he use?

4. You said the engine builder ran the engine with his electrics, which I presume means his ignition system. What system was that?

5. I've tried wading through the other post and the answer doesn't jump off at me. Are you experiencing these problems with the car sitting in your shop idling, or whilst driving the car?

6. I asked if you have hooked up a vacuum gauge and you replied in this post with what sound like cranking compression numbers. Have you had a vacuum gauge hooked up? If yes, what kind of readings did you record?

From everything you have written to date, a reasonable guess is your fuel pressure is excessive. But please note, that is nothing more than a guess. There's no way to know that is a problem, until you have actually checked it. So do yourself a favor and verify that number, before you move any farther. You can change everything under the sun, but none of those changes are going to work, if fuel pressure is excessive.

I'm really getting the impression all of this is being experienced with the car sitting in your shop. If it is, take all the advice about jet changes, step-up rod changes and spring changes and throw them out the window. When a car is idling, it is flowing fuel through the idle circuit and NOT the main jets. Get things working well on the idle circuit before you start making wholesale changes to the accelerator pump circuit and main jet circuit.

Ben gave you a good piece of advice on the progressive carb linkage. You are going to want to use progressive linkage. But you need to fix the problem you already have before you start down that path.

John offered a valuable suggestion. If you simply cannot see the light of day, call the Edelbrock tech line. Those people are getting paid to help you diagnose problems and fix them to your satisfaction. But you need to get your ducks in a row before you reach for the phone. Trust me, it can be nearly impossible to identify a problem, when a customer fails (or refuses) to provide real data. Those techs are going to ask you some specific questions and they are expecting you to give them specific answers. And trust me, one of the first questions they will ask is where fuel pressure is set. If you do not know the answer, they cannot diagnose anything. If you think fuel pressure is about this or that, you are not providing real data and the diagnostic process just came to an end. People would call and tell me they thought they had a 1.75 rocker ratio and their lobe lift was about .515" and their installed height was about 2.200". Which told me nothing, so my thought would turn to how the phone call was about over.

Tell us your fuel pressure setting. Tell us if you were present during the engine test. Tell us what intake and carb/s were used during that test. Tell us what ignition system he used, compared to what you are now using. Tell us if these problems are manifesting themselves in the shop, out on the open road or both. Tell us what kind of vacuum reading you have seen/recorded. And don't approximate anything, tell us real-world numbers, so we can evaluate what those numbers are telling us.

You can make things work, but you're going to have to leave the shotgun approach to someone else and get your focus narrowed down to identifying problems, one at a time. And then fixing them, one at a time. And ignoring everything else that might disrupt the process.
 
Zack, you're asking a lot of the same questions you were asking in the other thread.

What you're missing in the equation is that you need to provide some answers to some of the questions others have asked you.


Those were 500 CFM carbs in the other thread. Are they now, in fact, 600 CFM models?

You need to understand two facts. 1. That intake was not designed to be used on a street-driver. 2. You have far too much carburetor for what you're trying to do. You cannot escape those facts. All you can do is try to make things work as well as possible.

Step Number 1 - Quit trying to second-guess things.
Step Number 2 - Start testing things, so you will have hard data to work with, instead of guesses, ideas and generalities.



Answer? Who knows? Have you checked fuel pressure, to verify it is set at 6 psi or lower? Because that is quite likely the root of all your problems. But there is no way to know that for sure, because nobody knows where it is currently set.

So how can you change something, when you have absolutely no idea that is the cause of the problem?



Losing fuel balance to various cylinders. The common plenum on your intake choice will cover up some of the problem, but not all of it. You hide a lot of it by running on the rear carb alone, rather than the front carb alone, but balance will be affected.

If you feel disabling the front carb is the fix for your combination, you be absolutely sure you lock the throttle blades in the closed position. Otherwise, you're going experience over-heating, running lean and have all the fixings for a run-away motor.



You can tune what you have, so it will work reasonably well. Would you walk into a restaurant and order two steak dinners, when you have intentions of eating only one?



The mechanical secondaries on an Edelbrock carb shouldn't be confused with the mechanical secondary Holley carbs, which also use a secondary crutch, errr, accelerator pump. The secondary side of an Edelbrock carb is not going to flow any air/fuel until the weighted, secondary air valve opens.

Here are some specific questions for you -

1. Have you verified your fuel pressure setting? If not, why in the Dickens are you trying to sort what your problem might be? The problem might be (and likely is) excessive fuel pressure.

2. You said the engine builder ran this engine on a dyno or a test stand and that it ran fine. Did you have eyes and ears on this test session, or are you taking the engine builder's word at face-value?

3. You said the engine builder ran the engine with his intake. What intake was that? And what carburetor/s did he use?

4. You said the engine builder ran the engine with his electrics, which I presume means his ignition system. What system was that?

5. I've tried wading through the other post and the answer doesn't jump off at me. Are you experiencing these problems with the car sitting in your shop idling, or whilst driving the car?

6. I asked if you have hooked up a vacuum gauge and you replied in this post with what sound like cranking compression numbers. Have you had a vacuum gauge hooked up? If yes, what kind of readings did you record?

From everything you have written to date, a reasonable guess is your fuel pressure is excessive. But please note, that is nothing more than a guess. There's no way to know that is a problem, until you have actually checked it. So do yourself a favor and verify that number, before you move any farther. You can change everything under the sun, but none of those changes are going to work, if fuel pressure is excessive.

I'm really getting the impression all of this is being experienced with the car sitting in your shop. If it is, take all the advice about jet changes, step-up rod changes and spring changes and throw them out the window. When a car is idling, it is flowing fuel through the idle circuit and NOT the main jets. Get things working well on the idle circuit before you start making wholesale changes to the accelerator pump circuit and main jet circuit.

Ben gave you a good piece of advice on the progressive carb linkage. You are going to want to use progressive linkage. But you need to fix the problem you already have before you start down that path.

John offered a valuable suggestion. If you simply cannot see the light of day, call the Edelbrock tech line. Those people are getting paid to help you diagnose problems and fix them to your satisfaction. But you need to get your ducks in a row before you reach for the phone. Trust me, it can be nearly impossible to identify a problem, when a customer fails (or refuses) to provide real data. Those techs are going to ask you some specific questions and they are expecting you to give them specific answers. And trust me, one of the first questions they will ask is where fuel pressure is set. If you do not know the answer, they cannot diagnose anything. If you think fuel pressure is about this or that, you are not providing real data and the diagnostic process just came to an end. People would call and tell me they thought they had a 1.75 rocker ratio and their lobe lift was about .515" and their installed height was about 2.200". Which told me nothing, so my thought would turn to how the phone call was about over.

Tell us your fuel pressure setting. Tell us if you were present during the engine test. Tell us what intake and carb/s were used during that test. Tell us what ignition system he used, compared to what you are now using. Tell us if these problems are manifesting themselves in the shop, out on the open road or both. Tell us what kind of vacuum reading you have seen/recorded. And don't approximate anything, tell us real-world numbers, so we can evaluate what those numbers are telling us.

You can make things work, but you're going to have to leave the shotgun approach to someone else and get your focus narrowed down to identifying problems, one at a time. And then fixing them, one at a time. And ignoring everything else that might disrupt the process.

I am glad you chimed in Mike. As always you cover everything and i appreciate it. Yes, the carbs were sold to me as 500's. Once i checked the carb numbers i found the carbs were 600's. The sellers was not totally honest about alot of things on these. He said they were tuned and modified to run on a blower. When i went into them every thing (jets, rods, springs) were all stock. Nothing in these carbs has been modified as i was lead to believe from the seller.

1. Have you verified your fuel pressure setting? If not, why in the Dickens are you trying to sort what your problem might be? The problem might be (and likely is) excessive fuel pressure. No, Ron has a pressure regulator in the mail to me as we speak. I will be installing it and a gauge next week when it arrives.

2. You said the engine builder ran this engine on a dyno or a test stand and that it ran fine. Did you have eyes and ears on this test session, or are you taking the engine builder's word at face-value? Yes, i was there and ran it thru 1 full heat cycle until i was satisfied.

3. You said the engine builder ran the engine with his intake. What intake was that? And what carburetor/s did he use? Best i remember it was a Victor Jr. Style with a Holley 750DP and it ran better than most any other engine i have ever heard.

4. You said the engine builder ran the engine with his electrics, which I presume means his ignition system. What system was that? It was a standard GM HEI, nothing fancy, basically a stock setup.

5. I've tried wading through the other post and the answer doesn't jump off at me. Are you experiencing these problems with the car sitting in your shop idling, or whilst driving the car? Well, actually both but mostly while idling in the shop. Reving it up with hard quick blast it puffs a noticeable amount of black smoke and the exhuast gases are so strong they burn the crap out of my eyes in a matter of a minute or so.

6. I asked if you have hooked up a vacuum gauge and you replied in this post with what sound like cranking compression numbers. Have you had a vacuum gauge hooked up? If yes, what kind of readings did you record? No vacuum gauge yet, only a compression test. I will be getting a vacuum gauge next week to determine the vacuum.

All of what you have said here i do understand although it may seem like i don't. I have been working on and building the SBC's for may years but this is a first on a 2x4 setup and i am a bit skeptical with all the horror stories i have read online. If the TR didn't look so good on a bucket i would not run it but the looks are second only to a blower IMHO. I am counting on you guys to help as you all have/are. I appreciate every post made in my quest to gain more knowledge & suggestions about tuning a TR. As i stated, i will be trying to get some more numbers next week and go from there. The engine runs great except for the rich condition. Once that issue is under control it should perform as good as anyone could expect from a TR on the street. I will try to get some video of it running today that shows the black smoke. As always i really appreciate all the info. BTY, I will be ordering my progressive linkage today,
 
I could not agree more, but in this case, Zack isn't using an IR intake.


OK. Let's say "semi-IR" manifold. Although most of the tunnel ram manifolds have a plenum, it is small (unless you're using a really old one). It's going to be difficult getting a good air/fuel distribution running on the primary venturies of the back carb.

Edit to add: There should be some discussion of ignition timing also. But... Ron has it right. First step is to get the fuel pressure below 6psi. AFB carbs do not like lots of fuel pressure.
 
OK. Let's say "semi-IR" manifold. Although most of the tunnel ram manifolds have a plenum, it is small (unless you're using a really old one). It's going to be difficult getting a good air/fuel distribution running on the primary venturies of the back carb.

Edit to add: There should be some discussion of ignition timing also. But... Ron has it right. First step is to get the fuel pressure below 6psi. AFB carbs do not like lots of fuel pressure.

Thanks Photoman. Yes, this intake a 60's era (to be exact 1969) Weiand. I hope to get that regulator and gauge installed first of next week and that should tell the tale as far as fuel pressure is concerned.
 
<removes admin hat>

OK. Let's say "semi-IR" manifold. Although most of the tunnel ram manifolds have a plenum, it is small (unless you're using a really old one). It's going to be difficult getting a good air/fuel distribution running on the primary venturies of the back carb.

Sorry, but that's just silly talk. Since it has only undergone the addition of cocoa, does that mean chocolate ice cream is "semi-vanilla"? Individual runner intake and tunnel ram intake manifold are mutually exclusive terms.

By the true definition of the term, an individual runner intake has no plenum. Each cylinder is fed by its own, separate, independent and distinct intake runner. No matter how long or hard I look at that image of Zack's intake, I see all the runners joined at a common plenum. Let's instead say a spade is a spade and say "tunnel ram intake manifold". It's not a semi-IR any more than a cast-iron 2 bbl intake, it's not an almost-IR, it's not a close-to-IR, it's not a sort-of-IR, it is an intake where 8 intake runners derive fuel from a common plenum.

As for your comment on plenum size, might I suggest a bit of reading seems to be in order? Allow me to introduce you to Hermann Ludwig Ferdinand von Helmholtz. Well, he's actually dead these last 117 years, but if you're working with intake manifold designs (that actually work), you need to be familiar with the Helmholtz resonance theories.

Do you understand why the word "ram" is used in the term "tunnel ram intake manifold"? Do you understand what happens in an intake manifold when the intake valve closes? Do you realize the inertia of that fuel charge wave does not stop moving? Do you understand that wave is reflected by the backside of the valve? Do you understand that wave travels back up the runner to the plenum at a speed approaching the speed of sound? Are you aware that wave has different components, primarily, amplitude, frequency and negative pressure? Are you aware the plenum of an intake manifold is actually a Helmholtz resonance chamber? Are you aware the plenum actually serves as a resonance chamber, where our reflected wave resonates at a particular frequency and then develops additional energy? Are you aware as this air wave returns again to the runner, at speeds approaching the speed of sound, it is traveling at a higher frequency because of the positive pressure provided by the resonance chamber? Are you aware this process is constantly repeated as waves are reflected from closed valves? Are you aware several columns of waves are existent in the intake manifold and are being amplified as this process repeats, until the intake valve opens again? Are you aware that is the theory behind the design of a tunnel ram intake manifold, to continue building energy in these reflected waves, in order to amplify these reflected waves until they reach a much higher energy? Are you aware this is why a tunnel ram works so poorly at low engine speeds, because the plenum is actually creating high amplitude, high frequency, positive pressure waves, rather than low-pressure signals to allow the carb/s to work efficiently? Have you ever wondered why you see fuel standing off the top of a mechanical fuel injection's ram tubes at low RPM? Are you aware how deliberate port opening mis-matches can create a reversion dam and increase efficiency?

The trick to all this is having the maximum energy wave arrive at the intake valve at the precise instant it begins to open, creating yet another venturi effect and resulting in the mass flow rate being increased by the increased amplitude. Which is why you will see the tunnel ram intakes on different race cars using different runner lengths and different plenum volumes. A properly designed tunnel ram intake is actually an acoustic supercharger, at a very narrow RPM range, because the high amplitude, high frequency, positive pressure waves can actually run volumetric efficiency percentages up over 100%.

Proper intake manifold design will use the proper physical dimensions of the runner to provide a resonant point that is relative to valve timing and desired engine RPM, to create a high amplitude, high frequency and positive pressure wave that will arrive at the precise moment the intake valve opens, to allow this wave to increase cylinder filling and an correspondent increase in torque at that desired RPM. Plenum displacement will vary on different applications, but a good rule of thumb will be plenum displacement being equal to engine displacement on naturally aspirated engines, whereas a fuel injected combination might want that displacement increased by an additional 10% - 20%. The term "ram" is used in association with these intake manifold designs for a specific reason, aye?

Are you aware the starting point for a tunnel ram intake's plenum volume (actually displacement, as is the case when properly designed) for a naturally aspirated engine is approximately equal to engine displacement, in order to produce peak torque at the 5,000 to 6,000 RPM range? Are you aware plenum displacement might be as much as 120% of engine displacement, for a fuel injected application? I don't have the numbers in front of me, but as memory serves, Zack's intake has a plenum displacement of approximately 270 cubic inches. And you suggest that volume might be small? This is where careful calculation comes into play, because changing plenum dimensions and runner lengths will have direct effect on what RPM range the intake manifold will be the most efficient. Rule of thumb says runner length will work out to approximately 14 inches, from the back of the valve to the opening of the runner, to achieve maximum mass air flow at 6,000 RPM. Take into account a common street rod might want maximum torque to occur as easy as 3,000 RPM and that runner length jumps to 28 inches.

Out of simple curiosity, how many intake manifolds have you designed? How many have you actually built? And of what materials? For what specific applications? Have you ever cut a cast aluminum intake apart to modify it's inherent characteristics?

I've no clue why you're splitting hairs on this point, but we can take it a step further and say the standard firing order camshaft is not a good idea and is going to upset fuel distribution, so Zack should immediately disassemble the engine and install a 4/7 swap cam. Is progressive linkage 100% correct in this application? No, it is not, but the goal here is to what he has running acceptably well. The tunnel ram intake is not 100% optimal for this application, either, but it's what he has. 1200 CFM of carburetor is not 100% optimal for this application, either, but it's what he has. So it's going to take some band-aids to patch things up and get what he has working. And my personal experience shows this can be done, albeit with some sacrifices to performance potential, with techniques such as a progressive linkage set-up on his non-IR intake manifold.

I've spent nearly 40 years studying and applying engine design, but I'm always eager to learn more dynamic theory. If you genuinely feel you have something to teach me, please, be my guest.

And please take note I am posting this as a member of this forum, who is just tired of seeing misleading, erroneous and often contradictory content being posted under the guise of knowledge and fact, rather than posting as the administrator of the forum. I suppose I could have created an alternate forum account and posted from it, to avoid the illusory sting of a forum staffer coming down on you. But the fact remains I am also a member of this forum. Ben posted he has used a progressive linkage combination on an intake manifold with a considerably-smaller plenum displacement for thousands of miles, yet you say it's not right without offering a reasonable level of fact to support your statement? Do you suggest or propose Ben was somehow being less than truthful or propagating falsehoods? That's the straw that broke the camel's back and it's no more than your simple misfortune to have your name attached to it. I enjoy reasonable debate, so long as light outweighs heat in the discussions. But reasonable debate takes place where factual accuracy and reasonable consistency exist. Your statements are completely lacking on both counts. Which means reasonable debate starts to break down into little more than a pissing match. I know you're likely going to take this personally, which is not my actual intent. For that, I apologize, but as previously stated, I'm immensely tired of inaccurate information being passed off as being factual. Hopefully, the information in this post will give people some proven fact to encourage further study, rather than supply misinformation that will confuse them.

<dons admin hat>
 
Zack: if you haven't ordered the progressive linkage yet, I found an extra one still in the box at the shop today. We had it for a dual carb 390 project that never materialized (was for a customer). $40 shipped and its yours.

To add to the discussion, my intake is a middle to low-rise Offenhouser. The plenum is not huge, but it seems to do an effective job of mixing. I check my plugs several times a year and they all look pretty good--not too lean and not too rich, and not much difference between them.

Mike: have you had no coffee this morn, or too much? :laugh:
 
This one is for a 710 cubic inch big block chevy.........Just thought I would share.

With a plenum like a suitcase.

moparps.jpg


Likewise, on this early 500" Hemi intake.

hogan001.png


But look at the wee plenum on the Flattie intake.

Here's one I am suspecting had been though make-up and was doing a bit of "posing" for the camera -

williams001.jpg


That's one Jim Williams had done for a 400" Aussie Pro Stock motor. Look at the runner lengths. But then look at the number of plenum spacers stacked on it. o_O Huh?

For those wondering what a true IR intake looks like -

hogan002.png


hogan003.png


hogan004.png


Mike: have you had no coffee this morn, or too much? :laugh:

Define "too much". :whistling: In my world, we've yet to reach the threshold of "too much" coffee. :roflmao: For the record, I am currently on the second pot, which is about right, considering the time of day.
 
Zack: if you haven't ordered the progressive linkage yet, I found an extra one still in the box at the shop today. We had it for a dual carb 390 project that never materialized (was for a customer). $40 shipped and its yours.

To add to the discussion, my intake is a middle to low-rise Offenhouser. The plenum is not huge, but it seems to do an effective job of mixing. I check my plugs several times a year and they all look pretty good--not too lean and not too rich, and not much difference between them.

Mike: have you had no coffee this morn, or too much? :laugh:

I'll take it for sure. PM me your address and i will paypal you the funds or mail them. Thanks, I appreciate it
 
With a plenum like a suitcase.

moparps.jpg


Likewise, on this early 500" Hemi intake.

hogan001.png


But look at the wee plenum on the Flattie intake.

Here's one I am suspecting had been though make-up and was doing a bit of "posing" for the camera -

williams001.jpg


That's one Jim Williams had done for a 400" Aussie Pro Stock motor. Look at the runner lengths. But then look at the number of plenum spacers stacked on it. o_O Huh?

For those wondering what a true IR intake looks like -

hogan002.png


hogan003.png


hogan004.png




Define "too much". :whistling: In my world, we've yet to reach the threshold of "too much" coffee. :roflmao: For the record, I am currently on the second pot, which is about right, considering the time of day.

Dang it Mike, That is some wild looking stuff and very expensive i am sure.:cool:
 

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